1. Field of the Invention
The invention is directed to the hydraulic circuitry for an electrically actuated quick drop valve.
2. Description of the Prior Art
Large construction machines, such as bulldozers, use quick drop valves to quickly lower working implements. This allows the operator to quickly reposition the implement for the next operation and also to execute a "drop-and-catch" procedure to clear the implement of material adhering to the implement.
Typically these quick drop valves are spring biassed pilot operated valves. The valve spool is hydraulically balanced between two pilot control lines. One of the pilot lines is provided with a restriction so that there is a pressure differential between the two pilot control lines. A spring biasses the spool into a first position which allows the flow of fluid from the control valve to the hydraulic cylinder. As an operator actuates the blade control lever, to more quickly lower the blade, hydraulic pressure increases in the pilot control lines until the pressure in the control line opposite the spring overcones the spring and shifts the valve into a second position. In the second position the quick drop valve short circuits the flow of fluid from the lift side of the hydraulic cylinder to the reservoir and redirects it to the drop side of the hydraulic cylinder for quickly dropping the blade.
One problem of quick drop valves of the above-described configuration is that they are pressure, flow and viscosity sensitive. Therefore the exact shifting of the valve is not predictable.
Another deficiency is any differential pressure of sufficient magnitude to overcome the biassing spring will cause the valve to shift which may result in unexpected motion of the implement.